omap: TWL4030 Bump VMMC1 interface voltage from 3V to 3.15V

omap: TWL4030 Bump VMMC1 interface voltage from 3V to 3.15V

MMC interfaces are specified to be 3.3V compatible with an operating
voltage range of 3.1V to 3.5V for SD cards. This change affects
hardware using TWL4030 (TPS6595x) PMICs and should improve the
reliability when communicating with marginally-spec'd MMC devices.
3.15V is the highest possible level for this chip.  This patch
has been tested on a Gumstix Overo board.

Signed-off-by: Ash Charles <ash@gumstix.com>
Tested-by: Steve Sakoman <steve@sakoman.com>